Aviation Fuel Containing a Proportion of Organic Compunds from Biomass

ABSTRACT

The invention relates to an aviation fuel containing between 1 and 100 wt.-% of a fraction of a compound obtained by means of chemical transformation from renewable, natural optionally-hydroxylated monounsaturated fatty acids having a chain length at least equal to 14 carbon atoms, selected from among nitriles and medium fatty acid esters containing between 7 and 12 carbon atoms per molecule and between 0 and 99 wt.-% of a kerosene originating from petrol that meets global aviation fuel specifications.

A subject matter of the present invention is an aviation fuel (or kerosene) composed of a mixture of kerosene of oil origin and of a fuel derived from vegetable oils.

Aviation fuels have to meet a series of specifications resulting directly from the specific conditions (they are subject to extreme variations in temperature of some 80° C.) under which they are used. Within the range of the various current fuels, kerosene is presented as an intermediate petroleum fraction, in terms of distillation range, between gasoline and gas oil.

The three main technical characteristics of kerosene, in addition to its distillation range, are the density, the resistance to cold (melting point) and the flash point. There should also be added, to these characteristics, the energy requirement of the fuel, which is imperative for the satisfactory operation of the plane. This is because it is necessary to be able to have available a fuel having an energy requirement which is as high as possible while meeting the other characteristics.

It is possible, in the energy requirement, to distinguish the specific energy and the energy density. A high specific energy (energy requirement per kilogram) is important in order to minimize the energy consumption during takeoff when the tanks are full. A high energy density (energy requirement per liter) is important in order to minimize the volumes of tanks as any additional volume also implies an excess weight for the structure of the plane and tanks.

The aeronautical industry is a sector experiencing very strong growth, the development of which is dependent on the provision of fuel having oil as the sole source. As this fuel is on the way to disappearing in a few decades from now, manufacturers some years ago initiated studies to find replacement solutions.

The article by George Marsh, “Biofuels: Aviation Alternative” which appeared in “Renewable Energy Focus”, July/August 2008, pages 48 to 51, gives a broad panorama of the routes which are currently under exploration. For completeness with regard to the future of aviation, reflections may be added on the use of a fuel of another nature, such as hydrogen. However, the latter route would involve the design of new engines and thus the conceiving of a complete transformation of this industry. The routes which prevail today are those referred to in the English-speaking world as “drop-in”, that is to say which provide “synthetic” fuels which are compatible with current kerosene and which can thus be used in a mixture with the latter with the long-term objective of completely replacing it.

These studies, which have as objective the manufacture of a new renewable fuel, i.e. nonfossil fuel, are also part of the current preoccupation with limiting discharge of CO₂ to the atmosphere or more precisely of the limitation of the increase in CO₂ emissions to the atmosphere.

Mention may be made, among the routes of investigation, of synthetic fuels, which consist in chemically converting coal (CTL, for coal to liquid, according to the usual terminology) or gas (GTL, for gas to liquid) according to the Fischer-Tropsch synthesis. This synthetic route has been known for a very long time and is operational industrially. Its advantage is that the synthetic fuel, the hydrocarbon, is fully compatible with kerosene. However, it has many disadvantages.

First of all, the cost of the synthesis is high. Subsequently, the synthetic process is expensive in energy, which results in significant production of harmful CO₂. Finally, as the starting material is of fossil origin, it is not possible to speak of a source of renewable fuel.

As the main preoccupation is to find in the long term a permanent substitute for oil, it is necessary for the source (or the deposit) of this fuel to be renewable, which results in a search for carbon-rich crop products which will form biomass. To go further along this route, it is necessary to take into account an important additional parameter, mainly that this crop product or the cultivation of this product does not have an effect on the expansion of the cultivation intended for the feeding of man essential with the change in the world population.

To summarize, the selection of one of these routes naturally depends on the “thermal and energy” properties of the fuels thus obtained but also on three important additional criteria, namely the compatibility of these fuels with the engines currently used, the accordance with the new standards with regards to the emission of CO₂ and the harmonization (noncompetition) with food crops. The application of the first criterion results in provisionally leaving aside hydrogen, which would involve the development of new reactors, that of the second synthetic fuels based on fossil carbon, due to the production of CO₂ and that of the third a selection from carbon-rich plants intended for the production of an energy biomass not competing with food.

Currently, there does not truly exist a solution for manufacturing an aviation fuel derived from biomass which meets the regulations in place and which can be used in large amounts (greater than 10% by volume) as a mixture with kerosene.

In the biomass route, there exists, of course, the alcohol route, represented by ethanol and methanol, which are obtained by fermentation of sugars. Fuels based on such alcohols have been used, in particular in Brazil, for ground vehicles. They have also been used for light aviation but, due to their characteristics, they are simply not suitable for the manufacture of kerosene supplements or substitutes.

More important studies have been carried out using the knowledge developed in the context of biodiesel, a replacement fuel for gas oil for diesel engines. The basis of these studies was the use of vegetable oils obtained from seeds of various plants, such as rape, soya, sunflower, and the like, which are composed of a mixture of triglycerides of fatty organic acids, the chain length of which is generally between 16 and 18 carbon atoms.

In this context, a biofuel for diesel engines was developed which is known as Fatty Acid Methyl Ester (FAME), a predominant molecule of which is the methyl ester of oleic acid. The fatty acids are obtained from the seeds of these plants, from which their triglycerides are extracted, which triglycerides provide, by hydrolysis, the corresponding fatty acids which are subsequently esterified with methanol. The esters can be obtained by direct transesterification of the vegetable oil in the presence of methanol, which results in a mixture of esters. Similarly, FAEE, that is to say the corresponding ethyl ester essentially represented by oleic acid ethyl ester, was prepared. They form what is known as first-generation biodiesels. Second-generation biodiesels are also known, which products are obtained by hydrotreating the vegetable oils, resulting, by hydrogenation, in isomerized or nonisomerized long-chain hydrocarbons. The isomerization of the paraffins makes it possible to significantly reduce the cloud point, that is to say the temperature at which the paraffins begin to crystallize.

The proposal has also been made, in a paper by N.M. Irving published in the 16^(th) European Biomass Conference, 2-6 Jun. 2008, Valencia, Spain, under the title “Clean, High-Enthalpy Biofuels”, to replace, by nitrilation, the acid functional group of the fatty acid by a nitrile functional group. These fatty nitriles, obtained directly from natural fatty acids obtained by hydrolysis of the triglycerides present in the seeds, comprising chains of between C₁₂ and C₁₈ and centered mainly on C₁₆, appear to give excellent results in the biodiesel application.

Esterified or transformed fatty acids, such as FAME, which are conventionally known as biodiesels, constitute a fraction having boiling points, on the one hand, which are too high and melting points, on the other hand, which are also too high, these characteristics being related directly to the chain length of the fatty acid, conventionally from 16 to 18 carbon atoms, in order to be able to be incorporated in large amounts in aviation fuel fractions.

One solution might consist in using vegetable oils corresponding to shorter fatty chains, such as coconut, palm kernel or cuphea oils, for example. However, the esters of these vegetable oils then do not meet the criterion of density as they are too dense with respect to current fuels and do not meet the specifications with regard to energy requirement (specific energy) either. Another major disadvantage for the use of these oils is their relatively high cost.

The problem to be solved is thus that of finding a fuel based on a renewable source which meets as best as possible the criteria (specifications) of aviation fuels and in particular the criteria of density, of boiling and melting points and of energy requirement.

The invention is targeted at overcoming these disadvantages by providing aviation fuels composed of a mixture of a kerosene resulting from oil and of compounds chosen from nitriles and esters of medium fatty acids obtained from renewable monounsaturated fatty acids of natural origin, these medium fatty acids comprising from 7 to 12 carbon atoms per molecule.

This is because it has been discovered that fatty nitriles and fatty esters, having a medium chain length, might, by virtue of their characteristics of density, of boiling and melting points and of energy requirement, constitute a fraction which is particularly advantageous as aviation fuel.

In the continuation of the present description the use will be mentioned, as starting material, of natural and renewable, optionally hydroxylated, monounsaturated fatty acids. This term of fatty acid encompasses the acid proper, its ester form and its nitrile form. The change from an acid form to an ester form is entirely commonplace; the change from the acid form to the nitrile form is itself also well known, as will be explained later in the description. It is even perfectly possible to change to this nitrile form by direct treatment of the triglycerides present in natural oils or fats.

A subject matter of the invention is an aviation fuel comprising from 1 to 100% by weight of a fraction of a compound, obtained by chemical conversion starting from natural and renewable, optionally hydroxylated, monounsaturated fatty acids with a chain length at least equal to 14 carbon atoms, chosen from nitriles and esters of medium fatty acids comprising from 7 to carbon atoms per molecule, and from 0 to 99% by weight of a kerosene resulting from oil meeting the world specifications for aviation fuels.

The term “world specifications for aviation fuels” should be understood as meaning all of the specifications defined in the document “World Jet Fuel Specifications with Avgas Supplement”, 2005 edition, published by Exxon-Mobil. It covers, on the one hand, fuels of Jet type (Aviation Turbine Fuel—Jet A and Jet A1) and, on the other hand, “Military Turbine Fuel Grades” and “Aviation Gasolines”. This is because fuels of kerosene type exhibit the distinguishing feature of having to meet worldwide strictly the same specifications in order to ensure the safety of the transportations carried out.

In a preferred alternative form of the aviation fuel of the invention, this fraction of the compound will represent from 20 to 99% by weight and the kerosene meeting the world specifications from 1 to 80% by weight.

The choice of the respective contents will depend on the technical/economic conditions for supplying each of the constituents. However, it may be observed that some compounds do not meet, taken in isolation, the world specifications, which requires that they be used as a mixture with an ex-oil kerosene with proportions dictated by the difference between the characteristics of the compound and the specifications.

In another preferred alternative form of the invention, the fraction of the compound will be composed of a mixture of at least one of the nitrile and/or ester compounds and of at least one olefin and/or alkane comprising from 6 to 13, preferably from 7 to 12, carbon atoms per molecule, of natural origin, resulting from chemical conversions analogous to that applied to said natural and renewable, optionally hydroxylated, monounsaturated fatty acids. The portion of the olefin and/or alkane in the mixture constituting the fraction of the compound will represent from 10 to 50% by weight of the mixture.

This is because some molecules, alkanes or alkenes, with a chain length substantially analogous to that of the nitrile and/or ester compounds, that is to say comprising from 6 to 13 carbon atoms per molecule, can, if they are introduced into the fuel mixture, compensate for the “inadequacies” of the compound. This alternative embodiment might even make it possible in the long term to dispense with the use of kerosene. This route might become viable economically in particular in the case where the chemical treatments applied to the natural fatty acids comprising at least 14 carbon atoms would make possible, in addition to the synthesis of the nitrile and/or ester compound, the synthesis of such alkenes and/or alkanes.

It should be noted that these alkanes or olefins will be found in the final aviation fuel by the side of analogous molecules originating from the kerosene. However, it will be possible to distinguish them from one another due to the origin of the renewable hydrocarbons, which will comprise a ¹⁴C fraction.

In a preferred embodiment, the aldehyde is converted to acetal, or an acid, ester, nitrile, alcohol, alkane or olefin.

The compounds in their form of esters of medium fatty acids will preferably comprise an odd number of carbon atoms, 7, 9 or 11. The esters composed of 10 or 12 carbon atoms will preferably be in the form of an ω-unsaturated ester.

The compounds in their nitrile form will be in a saturated or monounsaturated form. The fatty nitrile comprising 12 carbon atoms will preferably be ω-unsaturated.

These fatty nitriles can comprise, according to some manufacturing processes, in addition to the nitrile functional group, another functional group, either ester or nitrile. These compounds can be introduced into the fuel if their characteristics (density, phase change temperatures and energy requirement) are sufficient not to have to subject them to a further and expensive conversion.

The alcohol radical participating in the ester functional groups will comprise from 1 to 4 carbon atoms. Preferably, this radical will be methyl in order to confer, on the compound, its best properties in the fuels of the invention.

The physical characteristics of the various molecules capable of participating in the composition of the aviation fuel of the invention are given in tables 1 to 3 below, which refer to the nitriles (table 1), to the esters or nitrile-esters (table 2) and to the olefins and alkanes (table 3).

TABLE 1 Density Molar mass g/ml Name Formula CAS g/mol Calc. Exp. Nitriles C₆ Nitrile CH₃(CH₂)₄—CN 628-73-9 97.158 0.803 0.8069 C₇ Nitrile CH₃(CH₂)₅—CN 629-08-3 111.158 0.808 C₈ Nitrile CH₃(CH₂)₆—CN 124-12-9 125.158 0.813 0.8198 C₉ Nitrile CH₃(CH₂)₇—CN 2243-27-8 139.158 0.816 0.8221 C₁₀ Nitrile CH₃(CH₂)₈—CN 1975-78-6 153.158 0.819 0.82945 2MeC₁₀ CH₃(CH₂)₇—CH(CH₃)—CN 69300-15-8 167.158 0.82 0.81851 C₁₁ Nitrile CH₃(CH₂)₉—CN 2244-07-7 167.158 0.822 0.8254 C₁₂ Nitrile CH₃(CH₂)₁₀—CN 2437-25-4 181.158 0.824 0.827 C₁₄ Nitrile CH₃(CH₂)₁₂—CN 629-63-0 195.158 0.827 C₁₀ = Nitrile CH₂═CH—(CH₂)₇—CN 61549-49-3 151.158 0.83 C₁₁ = Nitrile (1) CH₂═CH—(CH₂)₈—CN 53179-04-7 165.158 0.832 0.8443 C₁₁ = Nitrile (2) CH₃—(CH₂)₇—CH═CH—CN 22629-48-7 165.158 0.838 0.83255 C₁₁ = Nitrile CH₂═CH—(CH₂)₉—CN 179.158 Boiling Heat of Specific Energy point Melting Flash combustion energy density ° C. point point Name kJ/mol Source MJ/kg MJ/litre Calc. Exp. ° C. ° C. Nitriles C₆ Nitrile 164.5 162 −80 43.3 C₇ Nitrile 186 198 −64 60.5 C₈ Nitrile −5184.5 NIST −41.4 −33.9591 206.2 200 −45 73.9 C₉ Nitrile 205.2 224 −34 81.1 C₁₀ Nitrile −6492.1 NIST −42.4 −35.1589 243.2 243 −18 92 2MeC₁₀ 250.9 247 128.8 C₁₁ Nitrile −7145.3 NIST −42.7 −35.28237 253 255 −6 100.6 C₁₂ Nitrile 276.4 277 4 108.3 C₁₄ Nitrile 306.3 19 121.8 C₁₀ = Nitrile 252.3 112.1 C₁₁ = Nitrile (1) 270.3 122.8 C₁₁ = Nitrile (2) 252.4 106.5 C₁₁ = Nitrile Calc. corresponds to the calculated values and Exp. corresponds to the experimental values.

TABLE 2 Molar Density mass g/ml Name Formula CAS g/mol Calc. Exp. Esters C₆ Ester CH₃(CH₂)₄—COOCH₃ 106-70-7 130.185 0.882 0.87947 C₇ Ester CH₃(CH₂)₅—COOCH₃ 106-73-0 144.185 0.878 C₈ Ester CH₃(CH₂)₆—COOCH₃ 111-11-5 158.185 0.876 0.8775 C₉ Ester CH₃(CH₂)₇—COOCH₃ 1731-84-6 172.185 0.874 0.8655 C₁₀ Ester CH₃(CH2)₈—COOCH₃ 110-42-9 186.185 0.872 0.873 C₁₁ Ester CH₃(CH2)₉—COOCH₃ 1731-86-8 200.185 0.87 0.8708 C₁₂ Ester CH₃(CH2)₁₀—COOCH₃ 111-82-0 214.185 0.869 0.8702 C₁₀ = Ester CH₂═CH—(CH₂)₇—COOCH₃ 25601-41-6 184.185 0.883 C₁₁ = Ester CH₂═CH—(CH₂)₈—COOCH₃ 111-81-9 198.185 0.88 Nitrile ester C₁₁ CH₃OOC—(CH₂)₉—CN 133309-96-3 211.285 0.945 C₁₁═ CH₃OOC—(CH₂)₇—CH═CH—CN 173602-45-4 209.285 0.963 C₁₂ CH₃OOC—(CH₂)₁₀—CN 22915-49-7 225.285 0.938 Boiling Heat Specific Energy point Melting Flash of combustion energy density ° C. point point Name kJ/mol Source MJ/kg MJ/litre Calc. Exp. ° C. ° C. Esters C₆ Ester −4184 NIST −32.1 149.8 149.5 −71 45 C₇ Ester −4867.4 NIST −33.8 171 174 −56 52.8 C₈ Ester −5493.6 NIST −34.7 191.1 192.9 −36.7 72.8 C₉ Ester −6176.8 NIST −35.9 −31.0481 210.3 213.5 −34.2 84.4 C₁₀ Ester −6799 NIST −36.5 −31.8797 224 224 −13 94.4 C₁₁ Ester −7486.5 NIST −37.4 246.2 109.4 C₁₂ Ester −8117 NIST −37.9 −32.9781 263 267 5.2 114.5 C₁₀ = Ester 230.8 −33 90.6 C₁₁ = Ester 247.3 248 −27.5 99.3 Nitrile ester C₁₁ 312.3 145.5 C₁₁═ 314.2 146.6 C₁₂ 328.5 154.7 Calc. corresponds to the calculated values and Exp. corresponds to the experimental values.

TABLE 3 Molar Density Heat mass g/ml of combustion Name Formula CAS g/mol Calc. Exp. kJ/mol Olefins C₆ α-olefin CH₃(CH₂)₃—CH═CH₂ 592-41-6 84.17 0.672 C₈ α-olefin CH₃(CH₂)₆—CH═CH₂ 111-66-0 112.21 0.715 −5312.9 C₉ α-olefin CH₃(CH₂)₆—CH═CH₂ 124-11-8 126.22 0.734 C₁₀ α-olefin CH₃(CH₂)₇—CH═CH₂ 872-05-9 140.29 0.741 −5619 C₁₁ CH₃(CH₂)₈—CH═CH₂ 821-95-4 154.3 0.75 α-olefin C₁₂ CH₃(CH₂)₇—CH═CH₂ 112-41-4 168.32 0.768 −7925.9 α-olefin Alkanes C₆ Alkane CH₃(CH₂)₄CH₃ 110-54-3 86.18 0.659 −4163 C₈ Alkane CH₃(CH₂)₆CH₃ 111-65-9 114.22 0.703 −5430 C₁₀ Alkane CH₃(CH₂)₆CH₃ 124-18-5 142.3 0.73 −6778 C₁₂ Alkane CH₃(CH₂)₁₀CH₃ 112-40-3 170.33 −8086 Boiling Specific Energy point Melting Flash energy density ° C. point point Name Source MJ/kg MJ/litre Calc. Exp. ° C. ° C. Olefins C₆ α-olefin 61.9-65.8 −139.8 −26 C₈ α-olefin NIST −47.3478 −33.8537 119.9-123.9 −105.1-−99.1  C₉ α-olefin 141.9-149.9 −83.1-−80.9 C₁₀ α-olefin NIST −47.1808 −34.961 166.5-173.5 −68.1-−64.1 C₁₁ 186.9-198.9 −49.5-−48.8 α-olefin C₁₂ NIST −47.0883 −35.6929 212.5-213.8 −36.1-−34.1 α-olefin Alkanes C₆ Alkane NIST −48.3059 −31.8336 68.5-69.5 −96.1-−93.5 C₈ Alkane NIST −47.5398 −33.4205 125-127 −57.1-−56.4 +13 C₁₀ Alkane NIST −47.6318 −34.7712 174.1 −30.4-−29.2 C₁₂ Alkane NIST −47.4726 216 −10 Calc. corresponds to the calculated values and Exp. corresponds to the experimental values.

It may be observed that the α-olefins and alkanes exhibit certain characteristics (very low melting point, low density, high specific energy) which can constitute an excellent source for being incorporated as supplement of the mixture in a kerosene fraction. They make it possible in particular to compensate for the failings of certain compounds, such as esters, as regards density and specific energy. There is thus a specific advantage in keeping, as a mixture, the olefins and the unsaturated esters produced during the chemical conversion of the original fatty acid, in hydrogenating at the same time the olefins and the unsaturated esters in order to give an alkanes-saturated esters mixture. The combination of a nitrile compound and of an olefin or of an alkane will confer the same advantages on the mixture. The production of these two components can occur during the same reaction process provided that the fatty acid treated is in the nitrile form.

This solution is more advantageous than the normal solution, which consists in completely hydrogenating the vegetable oils, in that it consumes less hydrogen and also contributes to lowering the boiling points and solidification temperatures.

All the nitrile compounds exhibit a density entirely suitable for the use. As regards the energy requirement, it may be observed that the calorific value (specific energy), expressed in MJ/kg, for virtually all these nitriles is entirely analogous to that of standard Jet A1. In the field of the temperatures (boiling point, melting point and flash point), these compounds are overall within the standards. As regards the esters, their characteristics, even if they are not so good, are allowed then to be introduced in minor amounts into the fuels of the invention. Their shorter chain length than that of the esters of natural fatty acids of conventional oils (soya, rape, sunflower and even jatropha) renders them much more compatible with a Jet Fuel application, both from the viewpoint of the melting point (cloud point) and of the boiling points, for example.

The compounds of ester and/or nitrile type participating in the makeup of the fuel are obtained from monounsaturated fatty acids of natural and renewable origin. These fatty acids are higher acids, that is to say comprising at least 14 carbon atoms per molecule.

These fatty acids are in particular myristoleic (C₁₄═), palmitoleic (C₁₆═), petroselinic (C₁₈═), oleic (C₁₈═), vaccenic (C₁₈═), gadoleic (C₂₀═), cetoleic (C₂₂═) and erucic (C₂₂═) acids and the monohydroxylated fatty acids ricinoleic (C₁₈═OH) and lesquerolic (C₂₀═OH) acids.

The compounds participating in the makeup of the aviation fuel of the invention are obtained from natural oils (or fats) which are treated by hydrolysis or methanolysis in order to obtain fatty acids or their methyl esters as a mixture with glycerol, from which they are separated before chemical treatment. It is also possible to form the fatty nitriles directly from vegetable oils. It is particularly advantageous to form the nitrile from the oil when the latter is rich in free fatty acids, as in the case of used natural cooking oils or that of certain natural oils. It is preferable, in order to obtain the nitriles, to use fatty acids as starting material.

The conversions of the long-chain monounsaturated fatty acids/esters/nitriles are based on a fractioning of the long-chain molecule at the double bond. This fractioning will be carried out either by a cross metathesis reaction with ethylene (ethenolysis), or by oxidative cleavage of the double bond under the action of a strong oxidizing agent and in particular by oxidative ozonolysis, or by thermal cracking for hydroxylated fatty acids.

The ethenolysis reaction is often accompanied by an isomerization of the substrate and/or the products, which has the effect of resulting in a mixture of products. However, in the present use, the mixture of products is entirely compatible with the targeted application, which dispenses with the search for a catalyst which would not be at all isomerizing. The isomerization, for example in the case of the ethenolysis of the ester of oleic acid, has the effect of resulting in the formation of a mixture of esters of approximately 10 carbons and of a mixture of olefins, also of approximately 10 carbons. When, in the continuation of the present patent application, it will be indicated that a fuel comprises, besides kerosene, x % of a nitrile or ester compound (obtained via a metathesis) of “n” carbon atoms, this will mean that this compound will be a mixture composed of nitriles or esters comprising from n−2 to n+2 carbon atoms with a majority of compounds comprising n carbon atoms.

In an alternative form of the fractioning process, the cross metathesis can be carried out with acrylonitrile with formation, besides the α-unsaturated nitrile, of nitrile-ester difunctional compounds.

A few processing examples will be given by way of illustration of the various treatments for the conversion of these long-chain fatty acids to ester and/or nitrile compounds of the invention.

Myristoleic acid is subjected to an ethenolysis (cross metathesis with ethylene) according to the following reaction (the formulae are expressed in the acid form for the sake of simplicity of the account, even if the reaction involves the ester or the nitrile):

CH₃—(CH₂)₃—CH═CH—(CH₂)₇—COOH+CH₂═CH₂→CH₃—(CH₂)₃—CH═CH₂+CH₂═CH—(CH₂)₇—COOH

In a second stage, the C₆ α-olefin is optionally subjected to a cross metathesis reaction with the acrylonitrile in order to obtain a C₇ unsaturated nitrile according to the reaction:

CH₃—(CH₂)₃—CH═CH₂+CH₂═CH—CN→CH₃—(CH₂)₃—CH═CH—CN+CH₂═CH₂

The C₇ saturated nitrile is obtained by hydrogenation.

As was indicated above, the C₆ olefin can be introduced into the fuel mixture; it is also compatible with the application and can be hydrogenated to give hexane, itself also compatible.

Furthermore, the second product (acid) from the reaction forms, after esterification, a C₁₀ ω-unsaturated ester which can be used as is (or its formed saturated by hydrogenation) but which can also be converted via cross metathesis with acrylonitrile, according to a reaction analogous to that described above for the C₆ α-olefin, to give a C₁₁ unsaturated nitrile-ester.

It is also possible to carry out beforehand (before ethenolysis) the nitrilation of the myristoleic acid, which results, by ethenolysis, in the formation of the C₁₀ ω-unsaturated nitrile, besides the olefin.

Palmitoleic acid is subjected to an ethenolysis according to the following reaction:

CH₃—(CH₂)₅—CH═CH—(CH₂)₇—COOH+CH₂═CH₂→CH₃—(CH₂)₅—CH═CH₂+CH₂═CH—(CH₂)₇—COOH

In a second stage, the C₈ α-olefin is optionally subjected to a cross metathesis reaction with acrylonitrile in order to obtain a C₉ unsaturated nitrile according to the reaction:

CH₃—(CH₂)₅—CH═CH₂+CH₂═CH—CN→CH₃—(CH₂)₅—CH═CH—CN+CH₂═CH₂

The C₉ saturated nitrile is obtained by hydrogenation.

As was indicated above, the C₈ olefin can be incorporated in the fuel mixture. It can be hydrogenated beforehand.

The acid resulting from the ethenolysis reaction results in the same ester or nitrile-ester as in the case of myristoleic acid.

As for myristoleic acid, a nitrilation prior to the ethenolysis of the acid results in the formation of the C₁₀ ω-unsaturated nitrile.

Petroselinic acid is subjected to an ethenolysis according to the following reaction:

CH₃—(CH₂)₁₀—CH═CH—(CH₂)₄—COOH+CH₂═CH₂→CH₃—(CH₂)₁₀—CH═CH₂+CH₂═CH—(CH₂)₄—COOH

The C₁₃ unsaturated olefin can be incorporated as is as a mixture with the ester.

The C₇ ω-unsaturated acid results in the corresponding ester by esterification. In addition, by applying, to the latter, a metathesis reaction with acrylonitrile, a C₈ unsaturated nitrile-ester is obtained. By carrying out a cross metathesis with methyl acrylate, a C₈ unsaturated ester is obtained.

The prior nitrilation of the acid results, by ethenolysis, in the C₇ ω-unsaturated nitrile.

Oleic acid is subjected to an ethenolysis with the following reaction:

CH₃—(CH₂)₇—CH═CH—(CH₂)₇—COOH+CH₂═CH₂→CH₃—(CH₂)₇—CH═CH₂+CH₂═CH—(CH₂)₇—COOH

The C₁₀ unsaturated α-olefin is optionally subjected to a cross metathesis reaction with acrylonitrile in order to obtain a C₁₁ unsaturated nitrile according to the reaction:

CH₃—(CH₂)₇—CH═CH₂+CH₂═CH—CN→CH₃—(CH₂)₇—CH═CH—CN+CH₂═CH₂

The C₁₁ saturated nitrile is obtained by hydrogenation.

As indicated above, the C₁₀ olefin can be incorporated in the fuel mixture. It can be hydrogenated beforehand. The C₁₀ ω-unsaturated acid resulting from the ethenolysis can be esterified. The hydrogenation of the ester thus obtained makes it possible to obtain a C₁₀ ester. In addition, by applying a metathesis reaction with acrylonitrile to this ω-unsaturated ester, a C₁₁ unsaturated nitrile-ester is obtained.

The prior nitrilation of the acid results, by ethenolysis, in the C₁₀ ω-unsaturated nitrile.

Oleic acid can also be subjected to an oxidative cleavage, such as an oxidative ozonolysis, according to the following (simplified) reaction (the oxidative ozonolysis involves an oxygen source after the formation of the ozonide in order for the decomposition of the latter to result in two acid groups):

CH₃—(CH₂)₇—CH═CH—(CH₂)₇—COOH+O₃(O₂)→CH₃—(CH₂)₇—COOH+HOOC—(CH₂)₇—COOH

The C₉ ester is obtained after esterification of the monoacid.

Vaccenic acid is subjected to an ethenolysis according to the following reaction:

CH₃—(CH₂)₅—CH═CH—(CH₂)₉—COOH+CH₂═CH₂→CH₃—(CH₂)₅—CH═CH₂+CH₂═CH—(CH₂)₉—COOH

The C₈ unsaturated α-olefin is optionally subjected to a cross metathesis reaction with acrylonitrile in order to obtain a C₉ unsaturated nitrile according to the reaction:

CH₃—(CH₂)₅—CH═CH₂+CH₂═CH—CN→CH₃—(CH₂)₅—CH═CH—CN+CH₂═CH₂

The C₉ nitrile is obtained by hydrogenation.

As indicated above, the C₁₀ olefin can be incorporated in the fuel mixture. It can be hydrogenated beforehand.

The C₁₂ ω-unsaturated acid resulting from the ethenolysis can be esterified in order to obtain the C₁₂ ω-unsaturated ester.

The prior nitrilation of the acid results, by ethenolysis, in the C₁₂ ω-unsaturated nitrile.

Vaccenic acid can also be subjected to an oxidative cleavage, such as an oxidative ozonolysis, according to the following (simplified) reaction:

CH₃—(CH₂)₅—CH═CH—(CH₂)₉—COOH+O₃(O₂)→CH₃—(CH₂)₅—COOH+HOOC—(CH₂)₉—COOH

After esterification, on the one hand the C₇ is obtained and, on the other hand, the C₁₁ diester is obtained. This C₁₁ diester can be converted to nitrile, either completely, in order to form a dinitrile, or partially, in order to arrive at the nitrile ester. The dinitrile can also be formed from the diacid.

Gadoleic acid is subjected to an ethenolysis according to the following reaction:

CH₃—(CH₂)₉—CH═CH—(CH₂)₇—COOH+CH₂═CH₂→CH₃—(CH₂)₉—CH═CH₂+CH₂═CH—(CH₂)₇—COOH

The prior nitrilation of the acid results, by ethenolysis, in the C₁₀ ω-unsaturated nitrile.

The C₁₂ unsaturated α-olefin is optionally subjected to oxidative cleavage, such as an ozonolysis, according to the following (simplified) reaction:

CH₃—(CH₂)₉—CH═CH₂+O₃(O₂)→CH₃—(CH₂)₉—COOH+HCOOH.

The C₁₁ acid resulting from the ozonolysis is esterified to give C₁₁ ester and can, if appropriate, be converted to C₁₁ nitrile.

As indicated above, the C₁₂ olefin can be incorporated in the fuel mixture. It can be hydrogenated beforehand. The C₁₀ ω-unsaturated acid is esterified and then, if appropriate, hydrogenated to give C₁₀ saturated ester, it being possible, in either case, for the ester or acid functional group to be converted to a nitrile functional group.

This acid, after esterification with methanol, for example, can also be subjected to a cross metathesis reaction with acrylonitrile in order to obtain a C₂₂ unsaturated nitrile-ester according to the reaction:

CH₂CH—(CH₂)₇—COOMe+CH₂═CH—CN→CN—CH═CH—(CH₂)₇—COOMe+CH₂═CH₂

The C₁₁ nitrile-ester is obtained by hydrogenation.

Cetoleic acid is subjected to an ethenolysis according to the following reaction:

CH₃—(CH₂)₉—CH═CH—(CH₂)₉—COOH+CH₂═CH₂→CH₃—(CH₂)₉—CH═CH₂+CH₂═CH—(CH₂)₉—COOH

The prior nitrilation of acid results, by ethenolysis, in the C₁₂ ω-unsaturated nitrile.

The C₁₂ ω-unsaturated α-olefin is optionally subjected to an oxidative cleavage, such as an ozonolysis, according to the following (simplified) reaction:

CH₃—(CH₂)₉—CH═CH₂+O₃(O₂)→CH₃—(CH₂)₉—COOH+HCOOH.

The C₁₁ acid is esterified to give C₁₁ ester which can, if appropriate, be converted to C₁₁ nitrile.

The C₁₂ ω-unsaturated acid is esterified and then, if appropriate, hydrogenated to give C₁₂ saturated ester, it being possible for the ester or acid functional group in either case to be converted to a nitrile functional group.

Erucic acid is subjected to an ethenolysis according to the following reaction:

CH₃—(CH₂)₇—CH═CH—(CH₂)₁₁—COOH+CH₂═CH₂→CH₃—(CH₂)₇—CH═CH₂+CH₂═CH—(CH₂)₁₁—COOH

The C₁₀ unsaturated α-olefin is optionally subjected to a cross metathesis reaction with acrylonitrile in order to obtain a C₁₁ unsaturated nitrile according to the reaction:

CH₃—(CH₂)₇—CH═CH₂+CH₂═CH—CN→CH₃—(CH₂)₇—CH═CH—CN+CH₂═CH₂

The C₁₁ nitrile is obtained by hydrogenation.

The C₁₀ unsaturated α-olefin can also be subjected to an oxidative cleavage, such as an ozonolysis, according to the following (simplified) reaction:

CH₃—(CH₂)₇—CH═CH₂+O₃(O₂)→CH₃—(CH₂)₇—COOH+HCOOH.

The C₉ acid is esterified to give C₉ ester which can, if appropriate, be converted to C₉ nitrile.

As indicated above, the C₁₀ olefin can be incorporated in the fuel mixture. It can be hydrogenated beforehand.

Erucic acid can be subjected to an oxidative cleavage, such as oxidative ozonolysis, according to the following (simplified) reaction:

CH₃—(CH₂)₇—CH═CH—(CH₂)₁₁—COOH+O₃(O₂)→CH₃—(CH₂)₉—COOH+COOH—(CH₂)₁₁—COOH

The C₁₁ acid is converted to C₁₁ ester.

As regards the hydroxylated fatty acids, ricinoleic acid (C₁₈:1OH) and lesquerolic acid (C₂₀:1OH), the processes applied are slightly different.

In a preferred alternative treatment form, the methyl ester of ricinoleic acid is subjected to cracking according to the reaction:

CH₃—(CH₂)₅—CHOH—CH═CH—(CH₂)₇—COOCH₃(Δ)→CH₃—(CH₂)₅—CHO+CH₂═CH—(CH₂)₈—COOCH₃

The C₇ aldehyde is easily converted to C₇ acid by oxidation and then to C₇ nitrile, the formation of the aldehyde functional group being an intermediate phase in the conversion of the carboxyl functional group to a nitrile functional group.

The C₇ aldehyde can also be converted to dimethyl acetal by the action of methanol, which product can be incorporated in the fuel mixture in the same way as for the olefins or alkanes mentioned above.

The C₁₁ ω-unsaturated ester, methyl w-undecylenate, resulting from the cracking can be hydrolyzed to give w-undecylenic acid. The hydrogenation of the ester thus obtained makes it possible to obtain the C₁₁ ester. This ω-undecylenic acid can be converted to ω-undecylenic nitrile. In addition, by applying, to this ω-unsaturated ester, a metathesis reaction with acrylonitrile, a C₁₂ unsaturated nitrile-ester is obtained.

The same process, applied to lesquerolic acid, results in the reaction:

CH₃—(CH₂)₅—CHOH—CH═CH—(CH₂)₉—COOCH₃(Δ)→CH₃—(CH₂)₅—CHO+CH₂═CH—(CH₂)₁₀—COOCH₃

The C₇ aldehyde is easily converted to C₇ nitrile or converted to dimethyl acetal, as indicated above.

The processes used for carrying out the conversions described above are well known to a person skilled in the art.

The routes for the nitrilation of functional hydrocarbons (acids, aldehydes, alcohols) in order to convert them to a nitrile functional group are well known.

An example of an industrial process which uses a fatty acid as starting material is that of the manufacture of fatty nitriles and/or amines starting from fatty acids extracted from vegetable or animal oils. This process, which is described in the Kirk-Othmer Encyclopedia, vol. 2, 4^(th) edition, page 411, dates from the 1940s. The fatty amine is obtained in several stages. The first stage consists of a methanolysis or a hydrolysis of a vegetable oil or of an animal fat, respectively producing the methyl ester of a fatty acid or a fatty acid. The methyl ester of the fatty acid can subsequently be hydrolyzed to form the fatty acid.

Finally, the fatty acid is converted to the nitrile by reaction with ammonia (which will finally be converted to the amine by hydrogenation of the nitrile thus obtained).

The reaction scheme for the synthesis of the nitriles can be summarized in the following way:

Two types of process based on this reaction scheme exist: a liquid-phase batch process and a vapor-phase continuous process.

The processes use a nitrilation agent generally chosen from ammonia or urea and employ a metal oxide catalyst, such as ZnO or others.

Mention may also be made of the processes described in the patent U.S. Pat. No. 6,005,134 (Kao), targeting a catalytic process based on titanium oxide, the Japanese applications Nos. 10-178414 and 11-117990 (Kao), describing the use of niobium oxide, and the Japanese application No. 9-4965, targeting a catalyst based on zirconium dioxide.

Finally, note must be taken of the U.S. Pat. No. 4,801,730, which describes the synthesis of fatty acid nitriles in the presence of ammonia and of a catalyst based on organometallic sulfonates starting directly from the constituent triglycerides of an animal fat or of a vegetable oil, resulting in a mixture of glycerol and various fatty acid nitriles according to the nature of the feedstock.

The catalysis of the metathesis reaction has formed the subject of a great many studies and the development of sophisticated catalytic systems. Mention may be made, for example, of the tungsten complexes developed by Schrock et al. (J. Am. Chem. Soc., 108 (1986), 2771) or Basset et al. (Angew. Chem., Ed. Engl., 31 (1992), 628). More recently, “Grubbs” catalysts, which are ruthenium-benzylidene complexes, have appeared (Grubbs et al., Angew. Chem., Ed. Engl., 34 (1995), 2039, and Organic Lett., 1 (1999), 953). These relate to homogeneous catalysis. Heterogeneous catalysts have also been developed which are based on metals, such as rhenium, molybdenum and tungsten, deposited on alumina or silica. Finally, studies have been carried out on the preparation of immobilized catalysts, that is to say catalysts whose active principle is that of the homogeneous catalyst, in particular ruthenium-carbene complexes, but which is immobilized on an inactive support. The object of these studies is to increase the selectivity of the reaction with regard to the side reactions, such as “homometathesis” reactions between the reactants brought together. They relate not only to the structure of the catalysts but also to the effect of the reaction medium and the additives which may be introduced.

In the processes described above, use may be made of any active and selective metathesis catalyst. However, use will preferably be made of ruthenium-based catalysts.

The metathesis reaction is generally carried out at a low temperature of between 20 and 100° C.

These processes are also described in the application WO 08104722 on behalf of the Applicant.

One of the possible stages of the processes for the conversion of unsaturated fatty acids is the cleavage by attack at the double bond of the molecule in order to achieve a division of the double bond with formation of at least one terminal acid or aldehyde functional group. This involves an oxidative cleavage of the double bond of the molecule. This cleavage can be carried out using strong oxidizing agents, such as KMnO₄, ammonium chlorochromate, aqueous hydrogen peroxide solution and more particularly ozone, hence the term of ozonolysis widely employed. It can be carried out by cracking but only in the case where a hydroxyl radical is located in a position α to the double bond.

Reference may be made, concerning ozonolysis and more generally oxidative cleavage, to the following publications: “Organic Chemistry” by L. G. Wade Jr., 5th Edition, Chapter 8, Reactions of Alkenes, the paper by G. S. Zhang et al. in Chinese Chemical Letters, Vol. 5, No. 2, pp. 105-108, 1994, and the paper “Aldehydic Materials by the Ozonization of Vegetable Oils”, Journal of the American Oil Chemists' Society, Vol. 39, pages 496-500. Reference is made to the “Criegee” reaction mechanism, marked by the formation of an ozonide.

It is apparent that the use of this oxidative cleavage depends on the objectives desired, either oxidative ozonolysis, resulting in the formation of the acid functional group, or reductive ozonolysis, if it is desired to stop at the aldehyde stage. In the processes described above, oxidative cleavage will be chosen if the aim is the formation of the acid functional group or of a nitrile functional group.

The process of cracking ricinoleic and lesquerolic acids is carried out in accordance with the industrial process described in the work “Les Procédés de Pétrochimie” [Petrochemical Processes] by A. Chauvel et al. which appeared in Editions TECHNIP (1986), targeted at the synthesis of 11-aminoundecanoic acid, which comprises several stages.

The first consists of a methanolysis of castor oil in a basic medium, producing methyl ricinoleate, which is subsequently subjected to pyrolysis in order to produce, on the one hand, heptanaldehyde and, on the other hand, methyl undecylenate. The latter is changed to the acid form by hydrolysis.

Transesterification with methanol makes it possible to obtain the methyl ester, as described in the patent application FR 2 918 058. The ricinoleic acid triglyceride (castor oil) is transesterified by an excess of methanol in the presence of sodium methoxide. The ester is then vaporized at 225° C. and subsequently mixed with superheated steam (620° C.). The reaction is brief, approximately ten seconds. The methyl undecenoate is subsequently purified, first of all by cooling in the medium, which makes possible the extraction of the water, and then by a series of distillations, which makes possible the separation of the ester and of the reaction by-products.

The mixture is cracked in the presence of steam at a temperature of 620° C. The degree of the conversion of the methyl ester is 70%. The light fraction is subsequently separated at atmospheric pressure and that mainly composed of heptanaldehyde is subsequently separated by distillation at reduced pressure. Subsequently, the fraction composed predominantly of the methyl ester of undecylenic acid is distilled under a vacuum of 0.01 atm. Finally, the fraction rich in methyl esters of oleic and linoleic acids is distilled from the fraction comprising the unconverted methyl ester of ricinoleic acid, which is optionally recycled to the cracking stage. The light fraction is composed predominantly of methyl esters of oleic and linoleic acids.

Use may be made of any plant whose seeds give unsaturated fatty acids of greater than 14 carbon atoms. However, castor oil, which comprises more than 80% by weight of ricinoleic acid, and Jatropha curcas oil, which comprises from 30 to 50% by weight of oleic acid, are non-food oils which are of great interest in the current fuel versus food debate. Furthermore, these plants have yields per hectare which are particularly high, rendering them very attractive. They can also grow in very difficult soils and under conditions of low rainfall, hence where few food plants can be cultivated, which also limits competition with food applications.

The aviation fuels of the invention are illustrated by the following examples.

EXAMPLE 1 Preparation of the Nitrile of Oleic Acid

Use is made, in this case, of a commercial oleic acid fraction comprising 76.8% of oleic acid. The acid fraction is distilled under vacuum in order to concentrate the oleic acid fraction up to a content of 85%.

The nitrile preparation is a conventional industrial operation for the preparation of fatty amines.

A conventional charge of 25 kg of ZnO as catalyst per 40 tonnes of fatty acid (i.e. 0.0625%) is used. The operation is carried out with an ammonia flow rate of 1000 Sm³/h (i.e. 0.417 l/min.kg). The temperature of the reactor is gradually increased by approximately 1° C./min from 160° C. up to 305° C. The injection of ammonia is begun from 160° C. The reaction is maintained under these conditions for approximately 13 hours, until the acid number is less than or equal to 0.1 mg of KOH/g. During the reaction, the temperature of the dephlegmator is maintained at 130° C.

The conversion to nitrile is followed by a simple distillation, where the crude product is purified on a distillation column of Vigreux type, a topping of the distillate being carried out.

The acid number of the nitrile obtained is 0.030 mg KOH/g, the iodine number is 98 g I₂/100 g and the distillation yield is 90%.

The final product comprises approximately 85% of oleonitrile, 10% of stearic acid nitrile and 4% of palmitic acid nitrile.

EXAMPLE 2 Ethenolysis of the Oleonitrile

The oleonitrile of the preceding example is converted to 1-decene and decenoic acid nitrile by ethenolysis in the presence of the catalyst [1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene]dichloro[[2-(1-methylethoxy)phenyl]methylene]ruthenium, CAS [301224-40-8], the formula of which is given below. The operation is carried out in toluene at a concentration of 0.05M, with 0.5% of catalyst, at 50° C. After 22 hours, the conversion is more than 99% and the calculated selectivity is 42% for decene and 46% for decenenitrile.

The mixture thus obtained has a density of 0.78 g/ml and a cloud point of −50° C. It can be incorporated in kerosene according to the terms of the invention.

EXAMPLE 3 Preparation of the Nitrile of Undecylenic acid

Use is made of undecylenic acid originating from the Arkema factory at Marseille St Menet. The latter is prepared by hydrolysis of the methyl ester of undecylenic acid.

The procedure is as in the preceding example 1. However, the lower boiling point of the acid generates significant reflux, which does not make it possible to reach 300° C. After 12 hours, the reaction is still not complete as, at equal weight, there are more moles to be converted. The residual acidity is 0.2% after 18 hours.

After reacting for 21 hours at 264° C., the final acid number is 0.17 mg KOH/g. The crude product is purified by distillation as above. The distillation is carried out under a vacuum of 40 mbar, with a distillation yield of 83%.

The NMR analysis of the product shows that the double bond of the undecylenic acid nitrile has in part moved (isomerization reaction during the reaction). The final product comprises 96% of 10-undecenenitrile and 4% of isomers (where the C═C double bond is no longer terminal).

The mixture thus obtained has a density of 0.83 g/ml and a boiling point of 270° C. and can be incorporated in part in kerosene according to the terms of the invention.

EXAMPLE 4 Preparation of the Methyl Ester of Undecylenic Acid

The methyl ester of 10-undecylenic acid is synthesized according to the process described above (“Les Procédés de Pétrochimie” by A. Chauvel et al.).

The light fraction resulting from the final distillation is composed predominantly of the methyl esters of oleic and linoleic acids. This fraction, which represents approximately 15% of the castor oil, can be incorporated, in all or part, by the side of the methyl ester of 10-undecylenic acid, in the kerosene fraction.

The mixture thus obtained, comprising the methyl ester of undecylenic acid and the methyl esters of oleic and linoleic acids, has a density of 0.88 g/ml and a cloud point of −20° C. It can be incorporated in part in kerosene according to the terms of the invention.

The methyl ester of 10-undecylenic acid, used alone, can be incorporated in larger amounts in kerosene.

EXAMPLE 5 Preparation of the Methyl Ester of 9-Decenoic Acid by Etheneolysis

This example illustrates the ethenolysis of methyl oleate. Use is made, for this reaction, of the complex catalyst [RuCl₂(═CHPh)(IMesH₂)(PCy₃)], the formula (A) of which is given below. The reaction is carried out in CH₂Cl₂, at a methyl oleate concentration of 0.05M and an ethylene concentration of 0.2M, at a temperature of 55° C. and for 6 hours, in the presence of the catalyst at a concentration of 5 mol %, with respect to the methyl oleate. The yields are determined by chromatographic analysis. The methyl 9-decenoate CH₂═CH—(CH₂)₇—COOCH₃ and 1-decene yield is 55 mol %.

Catalyst of formula (A):

EXAMPLE 6 Preparation of the Methyl Ester of 9-Decenoic Acid by Ethenolysis

Experiments are carried out under an argon atmosphere in a glove box. The methyl ester of oleic acid (15 g), purified by filtration through activated alumina, is charged to a stirred glass reactor. A solution of 1000 ppm (content relative to the methyl ester) of the metathesis catalyst (reference 57972-6, CAS [172222-30-9], purchased from Sigma-Aldrich) in chlorine is prepared and is added to the methyl oleate. The reactor is equipped with a pressure probe and an introduction orifice. The closed system is removed from the glove box and connected to the ethylene line. The reactor is then purged 3 times with ethylene, then pressurized to 10 atm and placed in an oil bath at 40° C. for 2 hours. Before chromatographic analysis, the reaction is halted by adding a 1M solution of tris(hydroxymethyl)phosphine in isopropanol. The samples are then heated at 60° C. for 1 h, diluted in distilled water and extracted with hexane before analysis by gas chromatography. The analysis reveals a 1-decene yield of 30% and a methyl 9-decenoate yield of 30%.

The mixture of methyl ester of decenoic acid and of 1-decene can be used directly as fraction which can be incorporated in kerosene. It is also possible to leave a portion of the methyl ester of oleic acid in the mixture, which means that it is not necessary to look for high purity for the 1-decene plus methyl ester of 10-undecylenic acid fraction.

An equimolar mixture of methyl decenoate and 1-decene thus obtained has a density of 0.81 g/ml and a cloud point of −52° C. It can be incorporated in kerosene according to the terms of the invention.

EXAMPLE 7 Preparation of the Methyl Ester of Nonanoic Acid by Oxidative Cleavage

1 kg of oleic sunflower oil (82% of oleic acid, 10% of linoleic acid) is placed in a reactor with 5 g of tungstic acid and 50 g of hydroxylated oil originating from a preceding synthesis. The temperature is increased up to 60-65° C. and then 280 ml of a 50% aqueous hydrogen peroxide solution are added in 3 hours while flushing the reactor with nitrogen in order to limit the presence of water in the reactor and thus the dilution of the aqueous hydrogen peroxide solution.

Once the addition of the aqueous hydrogen peroxide solution has been completed, the reaction is continued for 3 hours. The mixture formed on conclusion of the preceding stage is placed in a stirred autoclave. 300 g of a 1% aqueous cobalt acetate solution (i.e. 0.4 mol % of Co, with respect to the diol produced in the preceding stage) are added. The temperature is adjusted to 70° C. and the reactor is placed under an air pressure of 12 bar. The start of the reaction is observed by the increase in temperature of the mixture because of the exothermicity of the reaction. The reaction then lasts 8 hours.

Subsequently, the aqueous phase is separated under hot conditions. The aqueous phase is separated from the organic phase. The recoverable aqueous phase comprises the catalysts of the preceding stages. The organic phase of the oxidized oil comprises the triglycerides of azelaic acid produced by the reaction, as a mixture with pelargonic acid. The distilled organic phase makes possible the recovery of a 360 g fraction of pelargonic acid and other short fatty acids.

The acid is subsequently esterified in the presence of methanol.

EXAMPLE 7a Preparation of Nonanoic Acid by Ozonolysis

This example illustrates the oxidative cleavage of oleic acid to give nonanoic acid by oxidative ozonolysis.

Ozone obtained by a Welsbach T-408 ozone generator is bubbled in 25 ml of pentane until a blue color is observed. The pentane solution is maintained at −70° C. with an acetone/dry ice bath. 20 mg of oleic acid dissolved in 5 ml of pentane and cooled to 0° C. are added to the ozone solution. The excess ozone is subsequently removed and the blue color disappears. After 5 minutes, the pentane is evaporated with a stream of dry nitrogen. During this stage, the temperature of the solution is maintained below 0° C. After evaporation of the pentane, 3 ml of methanol cooled to −70° C. are added to the reactor while reheating it in order to allow the ozonide to dissolve. In order to convert the ozonide to acid, the initial step is to raise the temperature to approximately 60° C. When the reaction of the decomposition of the ozonide begins, it is accompanied by a rise in the temperature. A stream of oxygen is continuously added, in order to maintain the temperature and to directly oxidize the products resulting from the decomposition of the ozonide. The procedure is carried out over 4 hours in order to limit the formation of decomposition products. It is important to maintain the reaction temperature slightly above the decomposition temperature of the ozonide during this stage. A temperature of 95° C. is used in this example.

6 mg of acid of formula CH₃—(CH₂)₇—COOH are obtained.

EXAMPLE 8 Esterification of the Nonanoic Acid

The nonanoic acid prepared according to example 7a is esterified by methanol with a stoichiometric excess of 100 in the presence of sulfuric acid as catalyst (2%). The reaction is carried out at reflux for 2 hours. At the end of the reaction, the methyl ester of nonanoic acid is isolated by extraction with the solvent, neutralization of the residual acids and then washing.

The methyl ester thus obtained has a density of 0.87 g/ml and a cloud point of −35° C. It can be incorporated in part in kerosene according to the terms of the invention.

Thus, in preferred embodiments of the invention:

-   -   the chosen ester is the methyl ester of 10-undecylenic or         undecanoic acid,     -   the chosen nitrile is the nitrile of decanoic acid or 9-decenoic         acid,     -   the chosen ester is methyl nonanoate,     -   the chosen nitrile is undecanenitrile or 10-undecenenitrile 

1. An aviation fuel comprising from 1 to 100% by weight of a fraction of a compound, obtained by chemical conversion starting from natural and renewable, optionally hydroxylated, monounsaturated fatty acids with a chain length at least equal to 14 carbon atoms, chosen from nitriles and esters of medium fatty acids comprising from 7 to 12 carbon atoms per molecule, and from 0 to 99% by weight of a kerosene resulting from oil meeting the world specifications for aviation fuels.
 2. The aviation fuel as claimed in claim 1, wherein the fraction of the compound will represent from 20 to 99% by weight and the kerosene meeting the world specifications for aviation fuels will represent from 1 to 80% by weight.
 3. The fuel as claimed in claim 1, wherein the fraction of the compound will be composed of a mixture of at least one of the nitrile and/or ester compounds and of at least one olefin and/or alkane comprising from 6 to 13 carbon atoms per molecule, of natural origin, resulting from chemical conversions analogous to that applied to said natural and renewable, optionally hydroxylated, monounsaturated fatty acids.
 4. The aviation fuel as claimed in claim 3, wherein the portion of the olefin and/or alkane in the mixture constituting the fraction of the compound will represent from 10 to 50% by weight of said mixture.
 5. The fuel as claimed in claim 1, wherein the esters of medium fatty acids comprise an odd number of carbon atoms.
 6. The fuel as claimed in claim 1, wherein the esters of medium fatty acids comprising 10 and 12 carbon atoms are ω-unsaturated.
 7. The fuel as claimed claim 1, wherein the fatty nitrile comprising 12 carbon atoms is ω-unsaturated.
 8. The fuel as claimed in claim 5, wherein the chosen ester is the methyl ester of 10-undecylenic or undecanoic acid.
 9. The fuel as claimed in claim 1, wherein the chosen nitrile is the nitrile of decanoic acid or 9-decenoic acid.
 10. The fuel as claimed in claim 5, wherein the chosen ester is methyl nonanoate.
 11. The fuel as claimed in claim 1, wherein the chosen nitrile is undecanenitrile or 10-undecenenitrile. 